Some users discovered this little "bonus" when playing through the demo, which released earlier today. The download contained the entire game and seems to have only really impacted the download from the North American PlayStation Store.
However, it seems as though the demo was pulled, at least temporarily, from all regions while it's sorted out. The original intent was to have the free download allow players to enjoy the opening parts of the game and then unlock the rest of the game come its release day on April 17. The idea being that the full game would already be on the hard drive and simply needed to be "unlocked" at the correct time.
Whoops!
This was originally going to be a news post about the demo being out, but I suppose that will have to come later once this is all sorted out.